An elevator system contains many moving and rotating parts, which are prone to malfunction. Parts can wear, they can be incorrectly installed, parts mounted in their intended position can move out of their position and movement subjects the parts to harmful vibration.
For this reason condition monitoring is needed in an elevator system, so that a malfunction can be predicted and so that a reaction can be effected before the fault itself appears and in the worst case stops the elevator.
The purpose of condition monitoring is to detect both changes that occur slowly and sudden deviations in the operation of a measuring device compared to earlier operation that is known to be normal. A condition monitoring appliance can also create a forecast or calculate the probability at a given moment for the occurrence of malfunction of a part of a device or a system. A condition monitoring appliance can also specify the optimal scheduling of servicing procedures or repair procedures. Without a special condition monitoring appliance it is possible to react to unusual operation of the system only after a fault has appeared and operation of the system has in the worst case been interrupted. With a condition monitoring appliance it is possible to react just before the malfunction or in the best case in good time before a malfunction would occur. By means of a condition monitoring appliance a special servicing procedure needed by the system can be scheduled in conjunction with a normal service visit.
Detecting faults and forecasting the malfunction of a device is called fault diagnostics. In fault diagnostics it is prior-art to measure phenomena caused by rotating parts such as vibration, noise, acoustic emissions and changes in stresses. These type of changes that occur over a long time span can be described as time series such that alarm limits can be set for measured magnitudes or for the magnitudes calculated for them, based on which it is possible to deduce the malfunction of a device occurring immediately or in the near future. In fault diagnostics prior-art methods also include the measurement of wear and the measurement of a change caused as a result of corrosion, wear or other use. The aforementioned phenomena for their part indirectly affect the functions of the device.
A condition monitoring system produces data about the functions of the elevator based on measurements. The essential functions to be measured are the timing of the operating cycle of the elevator, the number of starts from the different floors, the number of door re-openings, vibration of the elevator car and the door, friction on the door, noise levels at different stages of the operating cycle and parameters relating to ride comfort such as changes in the acceleration of the car.
For elevators a to-and-fro motion of the car occurring in one direction (a so-called translation motion) is characteristic, which differs from the operation of many machines and appliances. Additionally, the horizontal motion of the doors is characteristic for elevators. Operation is by its nature cyclical. The changes detected by condition monitoring of elevators in the operation of the parts of the elevator system can occur over a long time span quite slowly.
The vertically moving car and the horizontally opening and closing car doors and landing doors function as the most important moving parts of an elevator system. In the condition monitoring of an elevator it is essential that a deviation detected in some measured magnitude can be connected to the correct floor or to the location of the car in the elevator shaft.
Patent application FI20040104 discusses the condition monitoring of an automatic door e.g. in an elevator system. A dynamic model is created for the door, by means of which the frictional force exerted on the door is ascertained. From the magnitude of the frictional force, for its part, even a small disorder in the movement of the door and malfunction possibly preventing the operating capability of the door as a consequence can be seen.
Patent specification U.S. Pat. No. 5,476,157 presents an elevator control system, wherein the travel of the elevator car is monitored and controlled. The system comprises sensors monitoring each door of the floor levels, with which an open door is detected. Monitoring switches are also disposed at the landings, by means of which the floor location of the elevator car can be deduced. In the method movement of the elevator car is prevented in a situation in which one of the landing doors is open.
Publication JP2003112862 examines the vibrations of an elevator car. The acceleration of a vibration is determined with a detector. The acceleration data is controlled with an analyzer, in which the quality of ride comfort detected in the elevator car is deduced.
Publication JP2000313570 describes an elevator solution without machine room. Pulse transducers are situated in the system such that the motion data of the elevator is measured by means of the pulses transmitted. From this pulse data, for its part, the distance moved, the speed of the motion and the acceleration of the motion are generated for the elevator car. The data is utilized in the control of the elevators and in eliminating vibration of the car.
Publication JP9240948 presents a system, which forecasts malfunction of the elevator in advance. In the system numerous magnitudes relating to the elevator are measured, such as the speed of the elevator, acceleration, the speed of arriving at a floor level and the stopping position of the elevator at the floor level. By means of the data deductions are made by comparison with earlier measurement results. If the results differ from earlier ones by certain criteria, the malfunction situation to be forecast is deduced. The type of the forecast malfunction is notified to the user on screen and also to the computer administering the condition monitoring.
Publication JP8104473 investigates the changes occurring in an elevator system before an actual malfunction. The magnitude of a vibration is determined by examining the difference between the desired ideal speed of the car and the actual measured speed of the car. The magnitudes and types of the vibration in three different operating situations are recorded in the memory of the system. These three operating situations are the normal operating mode, the warning mode and the malfunction mode. By comparing the measured data and the data of the memory a possible change in the operation of the system is detected and a malfunction situation can thus be forecast and additional measurements can if necessary be made to verify the malfunction situation.
Publication U.S. Pat. No. 4,128,141 examines the speed of the elevator car as a function of position at a number of monitoring points in the elevator shaft. The measured speed signal is adjusted with a signal that is in proportion to the acceleration signal. By examining the adjusted speed signal malfunction relating to the movement of the car can be detected. In one embodiment of publication U.S. Pat. No. 4,128,141 the speed signal is derived in relation to time in order to achieve an acceleration signal.
In the detection by the condition monitoring appliance of a deviation in the magnitude describing the operation of the system, it is essential that the deviation data can be connected to the exact position of the elevator car in the elevator shaft. In prior-art technology the condition monitoring appliance has examined the data related to the operating situation of elevators at least partly directly from the control system. One problem with prior-art technology is that the location information of the elevator needed by fault diagnostics has not been determined very simply, i.e. additional sensors for measuring the position have been needed. A general condition monitoring appliance that is independent of the elevator system has not been available. Another problem is that in old elevator systems position information is difficult to obtain.